(1) Field of the Invention
This invention relates to a display apparatus connected to a host such as a graphics card in a computer for displaying images based on signals from the host.
(2) Description of the Related Art
Interface with a D-Sub connector, which is a typical type of analog interface, is chiefly used to connect a graphics card in a computer with a display apparatus.
The D-Sub connector is also called a 15-pin D-Shell display connector, a standard 15-pin VGA (Video Graphics Adapter) connector, or a VGA connector confirming to MIL-C-24308 Standard. In this specification, it will be called a VGA connector and the type of analog interface using this connector will be called a VGA interface. In this case, digital signals are converted to analog signals in the graphics card and the analog signals are transmitted to the display apparatus. The display apparatus processes the analog signals therein to display images.
Recently, it has become technically possible that display apparatus such as liquid crystal display apparatus accept digital signals as they are, and process and visualize these signals. Along with this trend, DVI-I, a digital interface using a new connector which is quite different from the VGA connector in shape, has been developed, and display apparatus having such interface are becoming commercially available.
DVI-I is the abbreviation of Digital Visual Interface Integrated which is the interface type that handles both TMDS (Transition Minimized Differential Signaling) digital signals and RGB (red, green and blue) analog signals.
A display apparatus having the DVI-I interface has a problem such that it cannot be physically connected to the graphics card having the VGA interface without a VGA/DVI-I conversion cable.
Even if the display apparatus is physically connected to the graphics card by using such a conversion cable, there is still another problem as mentioned hereinafter.
A computer operating system (hereinafter called an OS) today performs what is known as the Plug-and-Play function. Thus, when a Plug-and-Play compatible display apparatus is connected to a graphics card in a computer, the OS of the computer selects a driver (software) appropriate for display of images and automatically makes optimal settings for proper display.
To realize this function, the Plug-and-Play compatible display apparatus has specification information already stored in its memory, which is to be transmitted to the graphics card. This specification information is called EDID (Extended Display Identification Data), and includes, for example, the resolution, frequency of vertical scan signals, frame rate, vender code indicating the manufacturer's name, and the serial number of the display apparatus. Naturally, this information varies with models of display apparatus. Even display apparatus of the same model may have different information according to the interface type employed by the display apparatus.
Consequently, even when a graphics card having the VGA interface and a display apparatus having the DVI-I interface are connected through the conversion cable, EDID may not be transmitted normally to the graphics card. Even when EDID is transmitted, the Plug-and-Play function may not be performed normally. Then, no images will be displayed on the screen of the display apparatus, or appropriate display will not be achieved according to the specification of the display apparatus.